Conical scanning antenna



Aug. 19, 1958 J. L. BUTLER 2,843,715

CONICAL SCANNING ANTENNA Filed May 19, 1954 2 Sheets-Sheet 1 Jesse L.Butler mwzzvroze At'torney Aug. 19, 1958 J. L. BUTLER 2,848,715

CONICAL SCANNING ANTENNA Filed May 18, 1954 2 She'ets-Sheet 2 DOWN v E kl8 UP LEFT E (c) LEFT RIGHT l8 DOWN E UP Fig. 4

Jesse L. Butler INVENTOR.

CONICAL SCANNING ANTENNA Jesse L. Butler, Nashua, N. H., assignor, bymesne assignments, to Sanders Associates, Incorporated, Nashua, N. H., acorporation of Delaware Application May 19, 1954, Serial No. 430,924

10 Claims. (Cl. 343763) The present invention relates to the art ofradiating electromagnetic energy. More particularly, this inventionrelates to conical scanning antenna systems such as are used in certainsystems of radar.

In the prior art various systems have been proposed for developing aconical beam of electromagnetic energy by causing the beam to rotateabout the axis of the antenna system. This type of beam rotation isgenerally known as conical scanning in the art. It is to bedistinguished from the azimuth and elevation scanning functions of thesystem as awhole.

Conical scanning systems as employed in the prior art are usuallycharacterized by essentially unbalanced mechanical rotational systems.The speed which conical scanning requires in the most modern radartechniques has been unattainable by such systems.

In my copending application Serial Number 402,556, dated January 6,1954, the illuminator as shown in the preferred embodiment herein isdescribed.

It is, therefore, an object of the present invention to provide animproved, conical scanning, antenna system capable of ultra-high-speed,conical scanning.

It is a further object of the present invention to provide a rotatingconical scanning antenna system that is at all times electrically andmechanically balanced.

Other and further objects of the present invention will be apparent fromthe following description of a typical embodiment thereof, taken inconnection with the accompanying drawings.

In accordance with the invention, there is provided an antenna having anelectrically non-conductive rod forming a dielectric radiator. Surfaceelectromagnetic energy waves are propagated along the surface of the rodand sub-surface electromagnetic energy waves are propagated below thesurface of the rod. A reflecting means is disposed at the end of the rodfor causing the surface Waves and the sub-surface waves to be reflectedin phase. An annular member having three radiating elements with theircenters disposed substantially 120 apart is carried by the rod forradiating the waves.

In accordance with the invention, there is further provided a conicalscanning antenna. The antenna includes a source of plane-polarized,electromagnetic energy having a path of propagation. An annularradiating member is disposed coaxial with the path and has threeradiating elements circumferentially disposed at equal angles in a planeperpendicular to the path. Means are provided for effecting relativerotation between the direction of polarization of the energy and themember. Excitation of the radiating member by the energy develops an &-set beam of the energy which rotates about the path at a multiple of thefrequency of rotation of the direction of polarization to produce arotating beam of the energy and provide the conical scanning antenna.

In a particular embodiment there is provided an antenna comprising asource of electromagnetic energy for directive radiation and receptionof electromagnetic waves. An electrically conductive reflecting means inthe form 2,848,715 Patented Aug. 19, 1958 of a paraboloid providesdirectivity of radiation and reception. An illuminator for theparaboloid reflector is mounted axially and connected through itscenter. The illuminator comprises a nonconductive rod forming adielectric radiator along the surface of which and through which arepropagated the energy waves. An electrically conductive tube surroundspart of the rod adjacent one end thereof and provides a guide for theenergy wave. Adjacent the opposite end of the rod and substantially atthe focal point of the paraboloid, a reflector is provided havingconductive surfaces perpendicular to and surrounding the rod. Acylindrical portion at the center of the perpendicular surface surroundsthe end of the rod. An annular member is carried by the rod adjacent theperpendicular surface. The member comprises three radiating elementshaving their centers disposed substantially degrees apart. The novelantenna system disclosed in this specification is related to systemsdisclosed in concurrent applications Ser. Nos. 432,740 and 490,649 bythe same inventor. The present application is directed, in general, toan antenna system utilizing a novel annular radiator. The applicationSer. No. 490,649 is directed, in general, to an antenna system in whichthe electric vector of the electromagnetic energy is rotated withrespect to a stationary annular radiator by means of a rotating antennaelement. The application Ser. No. 432,740 is, in general, directed tothe broad concept of obtaining high-speed scanning by utilizing arotating electric vector in combination with a three element radiatingmember and, in particular, to the combination of an electromagneticgyrator to effect rotation of the electric vector with respect to theannular radiator.

In the accompanying drawings:

Fig. 1 is a schematic diagram illustrating conical scanning as providedby the present invention;

Fig. 2 is a side view, partly in section, of a preferred embodiment ofthe present invention;

Fig. 3 is an enlarged, detailed perspective view of a radiating memberas used in the embodiment of Fig. 2; and

Fig. 4 is a series of diagrams illustrating the operation of theinvention.

Referring now in more detail to the drawings and with particularreference to Fig. 1, an antenna system indicated at 1, is illustrated asradiating a beam 2 of electromagnetic energy, as shown. The main axis 3of the beam is caused to rotate about the antenna system axis orboresight 4, as illustrated. The rotating or circular motion of the beamaxis 3 is indicated by the path 5. The extreme lower position of thebeam is illustrated by the phantom lines 6. This rotation of the beamthus provides what is known as conical scanning.

Referring now to Fig. 2, the antenna of the present invention comprisesa primary dielectric radiator 7 (for example, a polystyrene rod)developing a beam of electromagnetic energy for the system. Atransmitter 8 is coupled to the radiator 7 through a cylindrical waveguide 9. The radiator 7 is divided into two sections, 7a and 7b, coupledtogether as shown. The section 7b is connected to a reflector 10 whichreflects energy in the direction of a paraboloidal reflector 11. Theparaboloid forms the energy into a beam that is radiated in thedirection as shown at 12. A motor 13 mechanically coupled through ashaft 14 to the reflector 10 causes the section 7b and the memberscarried by it to rotate. A metallic annular member 15 having three slotsformed therein is mounted on the radiator section 7b as shown. Themember 15 is located substantially at the focal point of the paraboloid11. The reflector 11 provides support for the motor assembly 13 throughthe support rods 16, connected as shown.

Referring now to Fig. 3 the radiating member 15 comprises threeradiating elements'16,- a half-wave length long at the operatingfi'equency, for example kilomegacycles, Theslots 17 are substantially aquarterwavelength deep at the operating frequency, as shown. Theslotsfunction electrically like resonant quarter-wavelength-transmission line sections and, therefore, present a very highimpedance across the opening although they are apparently shorted at theopposite ends. It is to be noted that the centers of each of theelements 16 and of each of the slots 17 are respectively disposedsubstantially 120 degrees apart.

Theoperation of the system can be better understood with particularreference to Fig. 4. For purposes of analysis, electromagnetic energyincident upon the member may be assumed to be plane polarized such thatits electric vector 18 or direction of polarization is veras describedwith respect tical as indicated. The energy radiated by the elements A,B and C of the member 15 maybe analyzed with respect to lines tangentthereto at their respective centers. A dipole (half-wave length element)radiates a maximum amount of energy when it is parallel to the directionof polarization or the electric vector, and a minimum or substantiallyzero when it is perpendicular to the electric vector. In particular,such an element radiates energy in accordance with the expression:

In the above expression, W equals the electromagnetic energy radiated bythe dipole having a direction of polarization or electric vectorparallel to the electric vector 18; k is a constant and 0 isthe anglebetween the dipole element and the electric vector 18. V

In this case the dipole elements are in the form of arcs of a circle andthe angle 0 may be taken as the angle between the line tangentto itscenter and the electric vector. For the elements A, B and C the angleswill be taken with respect to their tangent lines as shown.

Of particular significance in the present invention is thecharacteristic of the radiating member 15, whereby a single rotation ofthe member 15 through 360 degrees eifects three rotations of theresultant beam of energy as will be presently shown. In the diagrams athrough c the tangent lines of the respective elements are disposedsubstantially in the form of an equilateral triangle as shown; hence,the elements are disposed substantially 120 degrees, apart. The effectof increasing the radiation of the dipole element is to cause theresultant beam to be radiated in the direction of the element exhibitingmaximum radiation.

In'the diagram a the element A is positioned at zero degrees withrespect to the electric vector 18 and therefore radiates k units ofenergy. The elements B and C radiate .25k units of energy in accordancewith the expression for W above. Since the elements B and C aresymmetrically disposed about the horizontal axis and the element Aradiates the larger amount of energy to the right of the vertical axis,the resultant beam is directed to the right. a

In the diagram 12 the element A has been rotated 30 degrees. The elementA then radiates .75k units of energy and in symmetry the element B alsoradiates .751: units of energy. The element C being perpendicular to theelectric vector 18 radiates substantially zero energy. Since theradiation centers of the elements A and B are symmetrically disposedabout the vertical axis and below the horizontal axis, the resultantbeam is directed downward. v a p In the diagram 0 the element A has beenrotated 60 degrees with respect to the electric vector 18. The elementsA and C accordingly radiate .25k units of energy, while the element B,being parallel to the electric vector 18, radiates k units of energy.Since the element B is controlling, the main axis of the resultant beamwill be directed to the left. I p

"-ln' th'e diagram d the'e'lement A is shown rotated'90 degrees withrespect to the electric vector 18 and radiates substantially no energy.The elementsB and C radiate a total of 1.5k units of energy and sincetheir radiation centers are displaced above the center 0, theresultantbeam is displaced up as shown at 3 in Fig. 1. In the diagram 2 theelement A is shown rotated 120 degrees with respect to. the electricvector 18. The element C is now positioned such that the operation ofthe system to the element A above is repeated.

In the diagram 1 the locus of the main axis of the resultant beam due tothe rotation of radiating member 15 through an angle of 120 degrees isillustrated. The points W, X, Y and Z relate to the positions asillustrated by the diagrams a, b, c and d, respectively. By thisanalysis it is clear that the main axis of the beam rotates through 360degrees three times, while the radiating member 15 mechanically rotatesthrough 360 degrees one time.

' From the above description it is to be noted that the system asdescribed is inherently electrically and mechanically balanced. Sincethe motor, shaft and annular radiating member may be very light and aremechanically balanced, the physical speed of rotation may be soincreased that conical scanning rates may be increased from a typicalvalue of 50 cycles per second to as high as 1,000 cycles or more persecond.

While applicant does not intend to be limited to any particularparameters with respect to shape, size, speed or distances in theembodiment of the invention just described, the following relationshipsbetween the parts of the antenna system have been found to beparticularly suitable. The shaft 7 has a diameter of .625 inch and theradiating member 15 is disposed such that the end facing the exposedsurface of the reflector 10 is displaced .25 inch therefrom. The maximumouter diameter of the reflector 10 is 2 inches and the outer diam eterof the cylindrical wave guide 9 is .75 inch. The.

motor 13 is a synchronous motor and operates with a 400 cycle, 150 voltinput at a typical speed of 6,000 R. P. M. to produce a conical scanningrate of 300 cycles per second. The paraboloid has the general form of y=4fx, where f is equal to the focal length. The ratio between the focallength and the diameter at maximum opening is chosen to be .3 inch.Thus, if the desired maximum aperture is 20 inches the focus point ofthe parabola will be displaced 6 inches from its center.

The present invention greatly enhances the effectiveness of modern radartechniques as used in the detection and control of supersonic aircraft.

While there has been hereinbefore described what is at presentconsidered preferred embodiments of the invention, it will be apparentthat many and various changes and modifications may be made with respectto the embodiments illustrated, without departing from the spirit of theinvention. It will be understood, therefore, that all those changes andmodifications as fall fairly within the scope of the present invention,as defined in the surface Waves to be reflected in phase; and an annularmember carried by said rod for radiating said waves comprising threeradiating elements having their centers disposed substantially degreesapart.

' 2. An antenna comprising an electrically nonconductive rod forming adielectric radiator for propagating,

a o g he ?in???EF F P ,fi eetrem etiaea rsy. waves and below the surfacethereof sub-surface electromagnetic energy waves; a reflecting means atthe end of said rod for Causing said surface Waves and said subsurfacewaves to be reflected in phase; an annular membercarried by said rod forradiating said waves comprising three radiating elements having theircenters disposed substantially 120 degrees apart; and a paraboloidalreflector adjacent said member for forming said radiated waves into abeam.

3. In a conical scanning antenna, the combination of a source ofplane-polarized microwave energy; means for directing said energy alongan axis; a rotatable annular radiating member disposed in a planesubstantially perpendicular to and coaxially with said axis in the pathof said energy and having three elements circumferentially disposed 120apart varying in degree of radiation of said energy in accordance Withtheir angular positions relative to the direction of polarization ofsaid energy; and means for rotating said member about said axis to causethe resultant beam of said energy to rotate about said axis and effectsaid conical scanning at a frequency three times i that of the rotationof said member.

4. In a conical scanning antenna, the combination of a source ofplane-polarized microwave energy; means for directing said energy alongan axis; a rotatable annular radiating member disposed coaxially withsaid axis in the path of said energy and having formed therein threecircumferential slots disposed 120 apart, the degree of radiation ofsaid energy varying in accordance with the angular positions of saidslots relative to the direction of polarization of said energy; andmeans for rotating said member about said axis to cause the resultantbeam of said energy to rotate about said axis and eifect said conicalscanning at a frequency three times that of the rotation of said member.

5. in a conical scanning antenna, the combination of a source ofplane-polarized microwave energy; means for directing said energy alongan axis; a rotatable annular radiating member disposed coaxially withsaid axis in the path of said energy and having formed therein threenonradiating circumferential slots disposed 120 apart and axiallysubstantially one-quarter of a wavelength long at the operatingfrequency, the degree of radiation of said energy varying in accordancewith their angular positions relative to the direction of polarizationof said energy: and means for rotating said member about said axi tocause the resultant beam of said energy to rotate about said axis andeffect said conical scanning at a frequency three times that of therotation of said member.

6. In a conical scanning antenna, the combination of a source ofplane-polarized microwave energy; means for directing said energy alongan axis; an elongated, rotatable shaft disposed along said axis; arotatable annular radiating member carried by said shaft and disposedcoaxially with said axis, said member having three radiatin elementscircumferentially disposed 120 apart and varying in degree of radiationof said energy in accordance with their angular positions relative tothe direction of polarization of said energy; means for rotating saidshaft about said axis; and a parabolic reflector adjacent said member,said shaft passing centrally therethrough, to form a beam of said energywhereby rotation of said shaft and member about said axis causes saidbeam to rotate about said axis and effect said conical scanning at afrequency three times that of the rotation of said member.

7. A conical scanning antenna comprising the combination of a source ofplane-polarized microwave energy; an electrically non-conductive,rotatable, circular rod Cal - 6 forming a dielectric radiator along thesurface of which are propagated sub-surface waves to direct said energyalong an axis; a reflecting means at the end of said rod for causingsaid surface waves and said sub-surface waves to be radiated in phase;an angular member carried by said rod and disposed coaxially with saidaxis comprising three radiating elements transversely disposed apart andvarying in degree of radiation of said energy in accordance with theirangular positions relative to the direction of polarization of saidenergy; means for rotating said rod and member about said axis; and aparabolic reflector adjacent said member, said rod passing centrallytherethrough, to form a beam of said energy whereby rotation of said rodand member about said axis causes said resultant beam to rotate aboutsaid axis and effect conical scanning at a frequency three times that ofthe rotation of said member.

8. In an antenna a radiating member comprising an annular metallicmember; three like metallic radiating elements having the configurationof arcs less than 120 long extending axially from said member, saidelements being circumferentially disposed 120 apart; and like slotssubstantially one-quarter wave length long at the operating frequencyformed between the ends of said radiating elements and said member.

9. A conical scanning antenna comprising: a source of plane-polarizedmicrowave energy; means of directing said energy along an axis includingan elongated shaft having a rotatable section and a non-rotatablesection coupled to said source; an annular radiating member encirclingsaid rotatable section, said member having three radiating elementscircumferentially disposed 120 apart and varying in degree of radiationof said energy in accordance with their angular positions relative tothe direction of polarization of said energy; a parabolic reflectorhaving said non-rotatable section forming centrally therethrough; andmeans for rotating said rotatable section including brackets mounted onthe concave side of said reflector for supporting said rotatable sectionas an elongated extension of said non-rotatable section, wherebyrotation of said rotatable section forms a beam in said reflector whichrotates about said shaft to effect conical scanning at a multiple of thespeed of said rotatable section.

10. A conical scanning antenna, comprising: a source of plane-polarized,electromagnetic energy having a path of propagation; an annularradiating member coaxial with said path and having three radiatingelements circumferentially disposed at equal angles in a planeperpendicular to said path; and means for effecting relative rotationbetween the plane of polarization of said energy and said member,whereby excitation of said radiating member by said energy develops anoff-set beam of said energy which rotates about said path at a multipleof the frequency of said rotation, thereby producing a rotating beam ofsaid energy to provide said conical scanning antenna system.

References Cited in the file of this patent UNITED STATES PATENTS2,423,508 Leek July 8, 1947 2,531,455 Barrow Nov. 28, 1950 2,539,657Carter Jan. 30, 1951 OTHER REFERENCES Antennas (Kraus), published byMcGraW-Hill (New York), 1950 (page 429 relied on).

